The present invention relates generally to a fiber reinforced polyamide resin composite material and its manufacturing method and, more particularly, to a composite material which is suitable for use in molding articles and in which an adhesion between resin and reinforcing fibers is fast or firm to provide excellent mechanical strength, and a method for manufacturing such a composite material with high productivity.
By virtue of their light weight, excellent mechanical strength, corrosion resistance and so forth, various composite materials consisting of reinforcing fibers and thermoplastic resins are widely used for manufacture of electrical parts, auto parts, etc. It is well-known in the art that the fiber reinforced resin compositions for such uses are roughly divided into two types: one is a short-fiber reinforced pellet which is obtained by mixing short glass fibers with molten thermoplastic resin in an extruder, extruding therefrom the mixture in the form of a rod and cutting it into pellets of a predetermined shape; and the other is a long-fiber reinforced pellet which is obtained by impregnating long reinforcing fibers with molten thermoplastic resin, or liquid thermoplastic resin dissolved in a solvent, and then cutting it into a predetermined length.
The short-fiber reinforced pellet is defective in that it is inferior to the long-fiber reinforced pellet with regard to reinforcement effect, because the reinforcing fibers are cut short in the pelletization step and in the extruder during injection molding. On the other hand, manufacture of the long-fiber reinforced pellet involves problems such as difficulty in the impregnation of the long reinforcing fibers with the molten thermoplastic resin or, in case of impregnation with the thermoplastic resin in the form of a solution, difficulty in removal of the solvent and insufficient bond strength between the resin and the reinforcing fibers after the removal of the solvent.
As an improved method for impregnation of the resin into the reinforcing fibers, in particular, there is disclosed in H. Ishida and G. Rotter, "RIM-pultrusion of thermoplastic matrix composite," SPI 43rd Ann. Conf., 6-E (1988) a fiber reinforced nylon-6 RIM pultrusion method according to which two low-viscosity, reactive liquid monomers are mixed in a mixing chamber and the mixture is impregnated into the reinforcing fibers.
With the method disclosed in the above-mentioned literature, however, pot life after mixing the two liquids is relatively short. This poses a problem such as a limitation on the transfer of the mixture from the mixing chamber to an impregnation chamber or unbalanced supply of the mixture to the impregnation chamber. Besides, polymerization rate is low which results in low productivity, clogging of a die in the polymerization step and an increase in drawing resistance.
The inventors herein have been devoted to studying a fiber reinforced polyamide resin composite material and its manufacturing method which are free from the above-noted problems and, as the result of their studies, they have now made the present invention.